Scheduling in a Cellular Communication System Using a Large Excess Number of Base Station Antennas

ABSTRACT

The present disclosure is directed to a system and method for selecting a sub-group of user terminals (UTs) among a group of UTs served by a sector of a cellular network to schedule independent data streams for transmission to over the same time-frequency interval. In one embodiment, the sub-group of UTs is selected to limit inter-user interference among the sub-group of UTs. In another embodiment, the sub-group of UTs is selected to limit inter-user interference experienced by a UT that is at or near the boundary of the sector that serves the sub-group of UTs.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/943,022, filed Feb. 21, 2014, which is incorporatedby reference herein.

TECHNICAL FIELD

This application relates generally to scheduling in a cellularcommunication system that uses a large excess number of base stationantennas.

BACKGROUND

In a cellular communication system, multiple antennas at a base station(BS) and multiple antennas at one or more user terminals (UTs) served bythe BS allow two or more independent data streams to be transmitted fromthe BS to the UT(s) over the same time-frequency interval. The specifictransmission technique that makes this possible is referred to asspatial multiplexing. In general, spatial multiplexing is amultiple-input, multiple-output (MIMO) transmission technique that usesthe different “paths” or channels that exist between the multipleantennas at the BS and the multiple antennas at the one or more UTs tospatially multiplex the independent data streams over the sametime-frequency interval. When one UT is served two or more independentdata streams by the BS over the same time-frequency interval, the systemis said to be performing single-user MIMO (SU-MIMO), and when multipleUTs are each served one or more independent data streams by the BS overthe same time-frequency interval, the system is said to be performingmulti-user MIMO (MU-MIMO).

The number of independent data streams that can be transmitted over thesame time-frequency interval can be shown to be limited by the lesser ofthe number of antennas at the BS and the total number of antennas at theone or more UTs. A further limitation on the number of independent datastreams that can be transmitted over the same time-frequency intervalresults from interference between the independent data streams or whatis referred to as inter-user interference in the MU-MIMO context.

In T. L. Marzetta, “Noncooperative Cellular Wireless with UnlimitedNumbers of Base Station Antennas,” IEEE Transactions on WirelessCommunications, vol. 9, no. 11, pp. 3590-3600, Nov. 2010 [Marzetta], aconcept referred to as “massive MIMO” was introduced. In general terms,massive MIMO refers to a communication system that has a large number ofexcess antennas available at the BS over the number of independent datastreams to be transmitted over the same time-frequency interval. Theexcess antennas are used to reduce inter-user interference by furtherfocusing the energy of each independent data stream into ever-narrowerregions of space. This is done by appropriately shaping the independentdata streams so that the wave fronts emitted by the available antennasfor each of the independent data streams add up constructively at thelocation of the UT intended to receive the independent data stream anddestructively everywhere else (or at least everywhere else where anotherUT is intended to receive a different independent data stream over thesame time-frequency interval). The process of shaping the independentdata streams at the BS is known as precoding.

Although inter-user interference can be reduced using the concept ofmassive MIMO, for a practical number of excess antennas at the BS,inter-user interference can still affect downlink data transmissionswithout proper scheduling.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the embodiments of the presentdisclosure and, together with the description, further serve to explainthe principles of the embodiments and to enable a person skilled in thepertinent art to make and use the embodiments.

FIG. 1 illustrates an exemplary cellular network in which embodiments ofthe present disclosure can be implemented.

FIG. 2 illustrates a block diagram of an exemplary BS in accordance withembodiments of the present disclosure.

FIG. 3A illustrates an exemplary scenario in which scheduling can beused to reduce inter-user interference in accordance with embodiments ofthe present disclosure.

FIG. 3B illustrates another exemplary scenario in which scheduling canbe used to reduce inter-user interference in accordance with embodimentsof the present disclosure.

FIG. 3C illustrates another exemplary scenario in which scheduling canbe used to reduce inter-user interference in accordance with embodimentsof the present disclosure.

FIG. 3D illustrates another exemplary scenario in which scheduling canbe used to reduce inter-user interference in accordance with embodimentsof the present disclosure.

FIG. 4 illustrates a flowchart of a method for scheduling in a cellularcommunication system that uses a large number of excess transmitantennas in accordance with embodiments of the present disclosure.

FIG. 5 illustrates a block diagram of an example computer system thatcan be used to implement aspects of the present disclosure.

The embodiments of the present disclosure will be described withreference to the accompanying drawings. The drawing in which an elementfirst appears is typically indicated by the leftmost digit(s) in thecorresponding reference number.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the embodiments of thepresent disclosure. However, it will be apparent to those skilled in theart that the embodiments, including structures, systems, and methods,may be practiced without these specific details. The description andrepresentation herein are the common means used by those experienced orskilled in the art to most effectively convey the substance of theirwork to others skilled in the art. In other instances, well-knownmethods, procedures, components, and circuitry have not been describedin detail to avoid unnecessarily obscuring aspects of the disclosure.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of this discussion, the term “module” shall be understoodto include software, firmware, or hardware (such as one or morecircuits, microchips, processors, and/or devices), or any combinationthereof. In addition, it will be understood that each module can includeone, or more than one, component within an actual device, and eachcomponent that forms a part of the described module can function eithercooperatively or independently of any other component forming a part ofthe module. Conversely, multiple modules described herein can representa single component within an actual device. Further, components within amodule can be in a single device or distributed among multiple devicesin a wired or wireless manner.

I. Overview

The present disclosure is directed to a system and method for selectinga sub-group of UTs among a group of UTs served by a sector of a cellularnetwork to schedule independent data streams for transmission to overthe same time-frequency interval. In one embodiment, the sub-group ofUTs is selected to limit inter-user interference among the sub-group ofUTs. In another embodiment, the sub-group of UTs is selected to limitinter-user interference experienced by a UT that is at or near theboundary of a sector that is adjacent to the sector that serves thesub-group of UTs. These and other features of the system and method ofthe present disclosure are described further below.

II. System and Method for Scheduling Downlink Transmissions

FIG. 1 illustrates an exemplary cellular network 100 in whichembodiments of the present disclosure can be implemented. Cellularnetwork 100 is divided up into cells 102-106 that are each served by arespective base station (BS) 108-112. Each cell 102-106 can, in-turn, befurther divided up into sectors. For example, as shown in FIG. 1, cell102 is divided up into three sectors 102-1, 102-2, and 102-3. Cells102-106 and their associated sectors are geographically joined togetherto enable user terminals (UTs) 114 (e.g., mobile phones, laptops,tablets, pagers, or any other device with an appropriate wireless modem)to wirelessly communicate over a wide area with a core network 116 viaBSs 108-112. Cellular network 100 can be operated in accordance with anyone of a number of different cellular network standards, including oneof the current or yet to be released versions of the long-term evolution(LTE) standard and the worldwide interoperability for microwave access(WiMAX) standard.

For at least sector 102-1, BS 108 has an excess number of transmitantennas available to transmit independent data streams over the sametime-frequency interval to two or more UTs 114 located in sector 102-1.BS 108 is configured to use the excess transmit antennas in conjunctionwith precoding to appropriately shape the independent data streamsbefore they are transmitted to reduce interference between theindependent data streams or what is referred to as inter-userinterference. The excess transmit antennas are specifically used tofurther focus the energy of each independent data stream into narrowerregions of space in accordance with the concept of massive MIMO.

Referring now to FIG. 2, an exemplary block diagram of BS 108 isillustrated in accordance with embodiments of the present disclosure. BS108 includes, for transmitting downlink to UTs located in sector 102-1,N transmit antennas 202-1 through 202-N, a precoder 204, a data source206, and a scheduler 208.

As explained above in FIG. 1, BS 108 is configured to transmitindependent data streams over the same time-frequency interval to two ormore UTs 114 located in sector 102-1. BS 108 uses precoder 204 toprecode the independent data streams before they are transmitted toreduce inter-user interference. Several different precoding techniquescan be used, including matched-filter (MF) precoding, zero-forcing (ZF)precoding, minimum-mean square error (MMSE) precoding, and, with somemodifications to precoder 204, non-linear precoding techniques such asvector perturbation. In FIG. 2, the independent data streams arespecifically labeled s₁ through S_(K) and are provided to precoder 204by data source 206.

The precoded signal output by precoder 204 can be written as:

x=Σ_(i=1 to K) F _(i) s _(i),   (1)

where s_(i) is the independent data stream for the i-th UT, F_(i) is anNx1 precoding vector for the i-th UT, and K is the number of independentdata streams to be transmitted. Based on the precoded signal x beingappropriately fed to and transmitted by the N transmit antennas 202-1through 202-N, the symbol received by the UT intended to receive thek-th independent data stream s_(k) can be written as:

$\begin{matrix}\begin{matrix}{y_{k} = {{H_{k} \cdot x} + n_{k}}} \\{{= {{H_{k} \cdot {\sum_{i = {1\mspace{11mu} {to}\mspace{11mu} K}}{F_{i}s_{i}}}} + n_{k}}},}\end{matrix} & (2)\end{matrix}$

where n_(k) is a vector representing noise and H_(k) is a 1xN channelmatrix for the UT.

The symbol y_(k) includes interference from the symbols of theindependent data streams intended for other UTs. This component ofinterference, as explained above, is referred to as inter-userinterference and can be written as:

H _(k)·Σ_(i=1 to K) ^(i≠k) F _(i) s _(i)  . (3)

As noted above, BS 108 includes an excess number of transmit antennasover the number of independent data streams S₁ through S_(K) to betransmitted. BS 108 is configured to use the excess transmit antennas inconjunction with precoding to appropriately shape the differentindependent data streams before they are transmitted to reduceinter-user interference as given by Eq. (3). The excess transmitantennas are specifically used to further focus the energy of eachindependent data stream into narrower regions of space in accordancewith the concept of massive MIMO.

Although inter-user interference can be reduced using the concept ofmassive MIMO, for a practical number of excess transmit antennas at BS108, inter-user interference can still significantly affect downlinkdata transmissions without proper scheduling. Example scenarios whereproper scheduling can better leverage the narrower downlink beams toreduce inter-user interference are described below.

Referring now to FIG. 3A, a scenario is shown using exemplary cellularnetwork 100 described above in FIG. 1 where scheduling can be used tobetter leverage the narrower downlink beams provided by massive MIMO toreduce inter-user interference experienced by the at least three UTs114-1, 114-2, and 114-3 located in and served by sector 102-1.

As shown in FIG. 3A, UT 114-1 is located in close proximity to UT 114-3.Because UT 114-1 is located in close proximity to UT 114-3, downlinktransmissions to UT 114-1 are more likely to overlap and interfere withdownlink transmissions to UT 114-3 that occur over the sametime-frequency interval. Depending on how close UT 114-1 is to UT 114-3,the downlink transmissions to these two UTs may overlap and interfereeven with the narrower downlink beams provided by the excess transmitantennas at BS 108.

Therefore, in one embodiment, scheduler 208, further included in BS 108as shown in FIG. 2, can select a sub-group of UTs from among the UTsserved by sector 102-1 to transmit independent data streams to over thesame time-frequency interval based on the locations of the UTs. Inparticular, the sub-group of UTs can be selected based on the locationsof the UTs to limit inter-user interference among the sub-group of UTs.For example, scheduler 208 can include UTs in the sub-group of UTs thathave sufficient space between themselves and the other UTs included inthe sub-group of UTs. The amount of space deemed sufficient can bedetermined based on, for example, the number of excess transmit antennasavailable at BS 108 to transmit downlink to the UTs. This is becausemore excess antennas support the formation of narrower antenna beams. Inthe scenario shown in FIG. 3A, scheduler 208 may select UT 114-2 and114-3 to form, at least in part, one sub-group of UTs and select UT114-1 to form, at least in part, another sub-group of UTs because of itsclose proximity to UT 114-3.

Scheduler 208 can receive the locations of the UTs served by sector102-1 as input as shown in FIG. 2. The locations of the UTs served bysector 102-1 can be determined, for example, via triangulation using theglobal positioning system (GPS) satellites and/or via triangulationusing BSs in cellular network 100.

In addition to the above, if two or more UTs served by sector 102-1receive downlink transmissions from BS 108 at similar angles (relativeto the orientation of the BS antennas), downlink transmissions to thetwo or more UTs from BS 108 that occur over the same time-frequencyinterval are more likely to overlap and interfere.

Therefore, in another embodiment, scheduler 208 can select a sub-groupof UTs from among the UTs served by sector 102-1 to transmit independentdata streams to over the same time-frequency interval based on the angleat which downlink signals from BS 108 are received by the UTs. Inparticular, the sub-group of UTs can be selected based on the angle atwhich downlink signals from BS 108 are received by the UTs to limitinter-user interference among the sub-group of UTs. For example,scheduler 208 can include UTs in the sub-group of UTs that receivedownlink signals from BS 108 at sufficiently different angles than theother UTs included in the sub-group of UTs.

Scheduler 208 can receive the angles at which downlink signals from BS108 are received by the UTs served by sector 102-1 as input as shown inFIG. 2. As would be appreciated by one of ordinary skill in the art, theangle at which a downlink signal transmitted by BS 108 is received by aUT can be determined, for example, based on the angle at which an uplinksignal transmitted by the UT is received by BS 108, as these angles arelikely reciprocal.

After selecting a sub-group of UTs based on the location of the UTs orthe angle at which downlink signals from BS 108 are received by the UTs,scheduler 208 can schedule an independent data stream for each UT in thesub-group of UTs for downlink transmission over the same time-frequencyinterval. As shown in FIG. 2, scheduler 208 can specifically controldata source 206 to provide the independent data streams for each UT inthe sub-group of UTs at an appropriate time for precoding by precoder204 and downlink transmission by transmit antennas 202-1 through 202-N.

Referring now to FIG. 3B, another scenario is shown using exemplarycellular network 100 described above in FIG. 1 where scheduling can beused to better leverage the narrower downlink beams provided by massiveMIMO to reduce inter-user interference experienced by an edge UT 114-4served by sector 102-2 from downlink transmissions to one or more of theat least three UTs 114-1. 114-2, and 114-3 served by sector 102-1. Anedge UT, such as edge UT 114-4, is a UT that is at or near the edge of asector of a cell.

Typically, UTs in one sector of a cell experience negligible amounts ofinterference from the downlink transmissions to UTs in another, adjacentsector of a cell. This is because the energies of downlink transmissionsemitted by the transmit antennas of one sector are mainly containedwithin that sector and only low levels of energy from those downlinktransmissions permeate into adjacent sectors. However, for an edge UTthat is at or near the edge of the sector it is served by, the downlinktransmissions to UTs in the sector adjacent to the sector serving theedge UT can interfere with the edge UTs ability to receive downlinktransmissions.

Therefore, coordination techniques were developed to prevent thedownlink transmissions from the adjacent sector from interfering withthe downlink transmissions to the edge UT from its serving sector. Forexample, in one such coordination technique, the BS of the adjacentsector is prevented from transmitting downlink to the UTs of theadjacent sector over the same time-frequency interval that the BS of thesector serving the edge UT is transmitting downlink to the edge UT. Inanother coordination technique, the BS of the adjacent sector transmitsdownlink over the same time-frequency interval that the BS of the sectorserving the edge UT is transmitting downlink to the edge UT but with areduced power level to limit interference. In general, both techniquesrequire some coordination between the BSs of the two cells or, if thetwo sectors are served by the same BS, some coordination between thehardware used by the BS for each sector.

With the narrower downlink beams provided by massive MIMO, a differentcoordination technique involving scheduling can be implemented to reduceinter-user interference (also referred to as inter-sector interferencein this context) experienced by the edge UT 114-4 from downlinktransmissions to one or more of the at least three UTs 114-1, 114-2, and114-3.

For example, as shown in FIG. 3B, UT 114-3 served by sector 102-1 islocated in close proximity to UT 114-4 served by sector 102-2. BecauseUT 114-3 is located in close proximity to UT 114-4, downlinktransmissions to UT 114-3 are more likely to overlap and interfere withdownlink transmissions to UT 114-4 that occur over the sametime-frequency interval even with narrower downlink beams. Downlinktransmissions to the other UTs 114-1 and 114-2 are less likely tooverlap and interfere with downlink transmissions to UT 114-4 that occurover the same time-frequency interval because of the distance betweenthe UTs.

Therefore, in one embodiment, scheduler 208 can select a sub-group ofUTs from among the UTs served by sector 102-1 to transmit independentdata streams to over the same time-frequency interval that edge UT 114-4is scheduled to receive an independent data stream based on thelocations of the UTs. In particular, the sub-group of UTs can beselected based on the locations of the UTs served by sector 102-1 andthe location of edge UT 114-4 to limit inter-user interference at edgeUT 114-4. For example, scheduler 208 can include UTs in the sub-group ofUTs that have sufficient space between themselves and the edge UT 114-4.The amount of space deemed sufficient can be determined based on, forexample, the number of excess transmit antennas available at BS 108 totransmit downlink to the UTs served by sector 102-1.

In the scenario shown in FIG. 3B, scheduler 208 may select UT 114-1 and114-2 to form one sub-group of UTs and schedule independent data streamsfor transmission to those UTs over the same time-frequency interval thatedge UT 114-4 is scheduled to receive an independent data stream.Because of its close proximity to UT 114-4, scheduler 208 may furtherselect UT 114-3 to form, at least in part, another sub-group of UTs andschedule independent data streams for transmission to those UTs over adifferent time-frequency interval than edge UT 114-4 is scheduled toreceive an independent data stream to limit inter-user interference (orinter-sector interference) at edge UT 114-4.

Scheduler 208 can receive the locations of the UTs served by sector102-1 and the location of edge UT 114-4 as input. The location of edgeUT 114-4 can be sent to scheduler 208 via a message from the hardwareused by BS 108 to communicate with the UTs of sector 102-2. In additionto the location of edge UT 114-4, messages can be passed between therespective hardware used by BS 108 to communicate with the UTs ofsectors 102-1 and 102-2 to determine a time and/or frequency thatdownlink transmissions are scheduled to be transmitted to edge UT 114-4.This message passing between the respective hardware used by BS 108 tocommunicate with the UTs of sectors 102-1 and 102-2 can viewed as a typeof coordination between sectors 102-1 and 102-2.

It should be noted that edge UT 114-4 can be located on the edge of asector of a different cell than cell 102. For example, as shown in FIG.3C, edge UT 114-4 can be served by and located on the edge of a sectorin cell 106. The same scheduling technique described above can be usedto reduce inter-user interference (or inter-cell interference in thiscontext) experienced by edge UT 114-4 from downlink transmissions to oneor more of the at least three UTs 114-1, 114-2, and 114-3. The maindifference would be that the messages described above would be passedbetween BS 108 and BS 112.

Referring now to FIG. 3D, a scenario is shown again using exemplarycellular network 100 described above in FIG. 1 where scheduling can beused to better leverage the narrower downlink beams provided by massiveMIMO to reduce inter-user interference experienced by the at least threeUTs 114-1, 114-2, and 114-3 located in and served by sector 102-1 ofcell 102.

In general, as opposed to just selecting a sub-group of UTs from amongthe UTs served by sector 102-1 to transmit independent data streams toover the same time-frequency interval based on the locations of the UTs,as described above in FIG. 3A, FIG. 3D illustrates that selecting thesub-group of UTs based on locations of the UTs and the direction ofmovement of the UTs can be further beneficial. In particular, thedirection of movement of the UTs can be used to predicate whether twoUTs will eventually come in close proximity to each other such that thetwo UTs should not be selected to be a part of a sub-group of UTs toschedule independent data streams for transmission to over the sametime-frequency interval. Assuming two UTs eventually come in closeproximity to each other, the downlink transmissions to the two UTs mayoverlap and interfere even with the narrower downlink beams provided bythe excess transmit antennas at BS 108.

For example, FIG. 3D illustrates the location of UTs 114-1, 114-2, and114-3 and further illustrates a vector 118 that shows the direction ofmovement of UT 114-3. Scheduler 208 can select a sub-group of UTs fromamong the UTs served by sector 102-1 to transmit independent datastreams to over the same time-frequency interval based on the locationsof the UTs and the direction of movement of UT 114-3. In particular, thesub-group of UTs can be selected based on the locations of the UTs andthe direction of movement of UT 114-3 to limit inter-user interferenceamong the sub-group of UTs. For example, scheduler 208 can include UTsin the sub-group of UTs that have sufficient space between themselvesand the other UTs included in the sub-group of UTs and that arepredicted, based on their current direction of movement, to not come inclose proximity to one another. In the scenario shown in FIG. 3D,scheduler 208 may select UT 114-2 and 114-3 to form, at least in part,one sub-group of UTs but not include UT 114-1 in such a group because,based on the location of 114-3 and its current direction of movement, itmay come within close proximity to UT 114-1.

In another embodiment, the number of UTs in a sub-group to receiveindependent data streams over the same time-frequency interval can beadjusted or determined based on a speed of one or more UTs in thesub-group. If one or more UTs in the sub-group are moving fast, asdetermined for example based on some speed threshold, then the number ofUTs in the sub-group can be reduced. If, on the other hand, one or moreUTs in the sub-group are moving slow, as determined for example based onsome speed threshold, then the number of UTs in the sub-group can beincreased.

The average speed of one or more UTs in the sub-group can also be usedto determine or adjust the number of UTs in the sub-group that are toreceive independent data streams over the same time-frequency interval.For example, if the average speed is fast, as determined for examplebased on some speed threshold, then the number of UTs in the sub-groupcan be reduced. If, on the other hand, the average speed is slow, asdetermined for example based on some speed threshold, then the number ofUTs in the sub-group can be increased.

Finally, if the speed of a UT in the sub-group is above some speedthreshold, that UT can be removed from the sub-group and transmitted todownlink in an SU-MIMO mode to reduce inter-user interference. Scheduler208 can further perform the above noted adjustments based on speed.

In another embodiment, the beam widths associated with the downlinktransmissions to one or more of the UTs served by sector 102-1 can beadjusted. For example, the beam width of a downlink transmission to a UTserved by sector 102-1 can be adjusted based on a speed at which the UTis moving. If the UT is moving fast, it may be hard to continuallyupdate the direction of the beam of downlink transmission at the UT.Therefore, the beam width of the downlink transmission can be widened sothat the UT has a wider area over which to receive the downlinktransmission.

In another embodiment. the beam widths associated with the downlinktransmissions to one or more of the UTs served by sector 102-1 can beadjusted based on a desired downlink throughput and/or desiredreliability with which the downlink data is received by the UT. Ingeneral, widening the beam width may reduce the overall energy densityof the beam and downlink data rate to the UT, but may improve thereliability with which the downlink data is received by the UT, andnarrowing the beam width may increase the overall energy density of thebeam and downlink data rate to the UT, but may reduce the reliabilitywith which the downlink data is received by the UT.

In one embodiment, the beam width of a downlink transmission to a

UT is adjusted by adjusting the precoding vector used to precode thedownlink transmission to the UT. In another embodiment, the beam widthis adjusted by increasing or reducing the number of excess transmitantennas at BS 108 used to transmit downlink to the UT.

Referring now to FIG. 4, a flowchart 400 of a method for scheduling in acellular communication system that uses a large number of excesstransmit antennas is illustrated in accordance with embodiments of thepresent disclosure. The method of flowchart 400 can be implemented by BS108 as described above and illustrated in FIG. 2. However, it should benoted that the method can be implemented by other systems and componentsas well.

The method of flowchart 400 begins at step 402. At step 402, a sub-groupof UTs from among a group of UTs served a first sector of a cellularnetwork, such as sector 102-1 illustrated in FIG. 1, is selected tolimit inter-user interference. More specifically, as discussed above,the sub-group of UTs is selected to limit inter-user interference amongthe sub-group of UTs and/or to limit inter-user interference experiencedby a UT that is at or near the boundary of a sector that is adjacent tothe sector that serves the sub-group of UTs. For example, as discussedabove, the sub-group of UTs can be selected to serve one of thesepurposes based on a location of one or more UTs, an angle of arrival ofdownlink transmissions at one or more UTs, or a location and directionof movement of one or more UTs. After the sub-group of UTs is selected,flowchart 400 proceeds to step 404.

At step 404, a different data stream for transmission over a sametime-frequency interview is scheduled for each UT in the sub-group.

Finally, at step 406, the different data streams are precoded to produceprecoded data streams for transmission over the same time-frequencyinterval by more antennas than the number of precoded data streams.

It should be noted that, although the present disclosure was describedabove as being directed to a system and method for selecting a sub-groupof UTs to schedule independent downlink data streams for transmission toover the same time-frequency interval, it will be apparent to one ofordinary skill in the art based on the teachings herein that the samesystem and method with slight modifications can be used for selecting asub-group UTs to schedule independent uplink data streams fortransmission to over the same time-frequency interval.

III. Example Computer System Environment

It will be apparent to persons skilled in the relevant art(s) thatvarious elements and features of the present disclosure, as describedherein, can be implemented in hardware using analog and/or digitalcircuits, in software, through the execution of instructions by one ormore general purpose or special-purpose processors, or as a combinationof hardware and software.

The following description of a general purpose computer system isprovided for the sake of completeness. Embodiments of the presentdisclosure can be implemented in hardware, or as a combination ofsoftware and hardware. Consequently, embodiments of the disclosure maybe implemented in the environment of a computer system or otherprocessing system. An example of such a computer system 500 is shown inFIG. 5. Modules depicted in FIGS. 1 and 2 may execute on one or morecomputer systems 500. Furthermore, each of the steps of the flowchartdepicted in FIG. 4 can be implemented on one or more computer systems500.

Computer system 500 includes one or more processors, such as processor504. Processor 504 can be a special purpose or a general purpose digitalsignal processor. Processor 504 is connected to a communicationinfrastructure 502 (for example, a bus or network). Various softwareimplementations are described in terms of this exemplary computersystem. After reading this description, it will become apparent to aperson skilled in the relevant art(s) how to implement the disclosureusing other computer systems and/or computer architectures.

Computer system 500 also includes a main memory 506, preferably randomaccess memory (RAM), and may also include a secondary memory 508.Secondary memory 508 may include, for example, a hard disk drive 510and/or a removable storage drive 512, representing a floppy disk drive,a magnetic tape drive, an optical disk drive, or the like. Removablestorage drive 512 reads from and/or writes to a removable storage unit516 in a well-known manner. Removable storage unit 516 represents afloppy disk, magnetic tape, optical disk, or the like, which is read byand written to by removable storage drive 512. As will be appreciated bypersons skilled in the relevant art(s), removable storage unit 516includes a computer usable storage medium having stored therein computersoftware and/or data.

In alternative implementations, secondary memory 508 may include othersimilar means for allowing computer programs or other instructions to beloaded into computer system 500. Such means may include, for example, aremovable storage unit 518 and an interface 514. Examples of such meansmay include a program cartridge and cartridge interface (such as thatfound in video game devices), a removable memory chip (such as an EPROM,or PROM) and associated socket, a thumb drive and USB port, and otherremovable storage units 518 and interfaces 514 which allow software anddata to be transferred from removable storage unit 518 to computersystem 500.

Computer system 500 may also include a communications interface 520.Communications interface 520 allows software and data to be transferredbetween computer system 500 and external devices. Examples ofcommunications interface 520 may include a modem, a network interface(such as an Ethernet card), a communications port, a PCMCIA slot andcard, etc. Software and data transferred via communications interface520 are in the form of signals which may be electronic, electromagnetic,optical, or other signals capable of being received by communicationsinterface 520. These signals are provided to communications interface520 via a communications path 522. Communications path 522 carriessignals and may be implemented using wire or cable, fiber optics, aphone line, a cellular phone link, an RF link and other communicationschannels.

As used herein, the terms “computer program medium” and “computerreadable medium” are used to generally refer to tangible storage mediasuch as removable storage units 516 and 518 or a hard disk installed inhard disk drive 510. These computer program products are means forproviding software to computer system 500.

Computer programs (also called computer control logic) are stored inmain memory 506 and/or secondary memory 508. Computer programs may alsobe received via communications interface 520. Such computer programs,when executed, enable the computer system 500 to implement the presentdisclosure as discussed herein. In particular, the computer programs,when executed, enable processor 504 to implement the processes of thepresent disclosure, such as any of the methods described herein.Accordingly, such computer programs represent controllers of thecomputer system 500. Where the disclosure is implemented using software,the software may be stored in a computer program product and loaded intocomputer system 500 using removable storage drive 512, interface 514, orcommunications interface 520.

In another embodiment, features of the disclosure are implementedprimarily in hardware using, for example, hardware components such asapplication-specific integrated circuits (ASICs) and gate arrays.Implementation of a hardware state machine so as to perform thefunctions described herein will also be apparent to persons skilled inthe relevant art(s).

IV. Conclusion

Embodiments have been described above with the aid of functionalbuilding blocks illustrating the implementation of specified functionsand relationships thereof. The boundaries of these functional buildingblocks have been arbitrarily defined herein for the convenience of thedescription. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the disclosure that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent disclosure. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. it is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

What is claimed is:
 1. A method, comprising: selecting a subgroup of user terminals (UTs) from among a group of UTs served by a first sector to limit inter-user interference at an edge UT served by a second sector; scheduling, for each UT in the subgroup of UTs, a different data stream for transmission over a same time-frequency interval; and precoding the different data streams to produce precoded data streams for transmission over the same time-frequency interval by more antennas than the number of precoded data streams.
 2. The method of claim 1, wherein selecting the subgroup of UTs further comprises: selecting the subgroup of UTs based on a location of each UT in the group of UTs and a location of the edge UT.
 3. The method of claim 1, wherein selecting the subgroup of UTs further comprises: selecting the subgroup of UTs based on a message received from the second sector.
 4. The method of claim 3, wherein the message is transmitted from the second sector to the first sector.
 5. The method of claim 3, wherein the message is transmitted from a cell of the first sector to a cell of the second sector.
 6. The method of claim 3, wherein the message comprises a location of the edge UT.
 7. The method of claim 3, wherein the message comprises a time that a data stream is scheduled to be transmitted to the edge UT.
 8. The method of claim 1, wherein the first sector and the second sector are in a same cell.
 9. The method of claim 1, wherein the first sector and the second sector are in different cells.
 10. The method of claim 1, wherein the edge UT is closest to an edge of the second sector that is adjacent to an edge of the first sector.
 11. A system, comprising: a scheduler configured to schedule, for each UT in a subgroup of UTs, a different data stream for transmission over a same time-frequency interval, wherein the scheduler selects the subgroup of UTs from among a group of UTs served by a first sector to limit inter-user interference at an edge UT served by a second sector; and a precoder configured to precode the different data streams to produce precoded data streams for transmission over the same time-frequency interval by more antennas than the number of precoded data streams.
 12. The system of claim 11, wherein the scheduler is further configured to select the subgroup of UTs from among the group of UTs served by the first sector based on a location of each UT in the group of UTs and a location of the edge UT.
 13. The system of claim 11, wherein the scheduler is further configured to select the subgroup of UTs from among the group of UTs served by the first sector based on a message received from the second sector.
 14. The system of claim 13, wherein the message is transmitted from the second sector to the first sector.
 15. The system of claim 13, wherein the message is transmitted from a cell of the first sector to a cell of the second sector.
 16. The system of claim 13,—wherein the message comprises a time that a data stream is scheduled to be transmitted to the edge UT.
 17. A method, comprising: selecting a subgroup of user terminals (UTs) from among a group of UTs served by a first sector based on a location of a UT in the group of UTs served by the first sector to limit inter-user interference at an edge UT served by a second sector; scheduling, for each UT in the subgroup of UTs, a different data stream for transmission over a same time-frequency interval; preceding the different data streams to produce precoded data streams for transmission over the same time-frequency interval by more antennas than the number of precoded data streams.
 18. The method of claim 17, wherein selecting the subgroup of UTs further comprises: selecting the subgroup of UTs based on a message received from the second sector.
 19. The method of claim 18, wherein the message comprises a location of the edge UT.
 20. The method of claim 18, wherein the message comprises a time that a data stream is scheduled to be transmitted to the edge UT. 